Sulphurizing treatment of iron and steel



July 25, 1967 Fil'ed Oct. 8, 1963 FIG.

FIG.

United States Patent 3,332,809 SULPHURIZING TREATMENT OF IRON AND STEELYukio Tanaka, Tokyo-to, Akira Furusawa, Yokohamashi, and Kosaku Isobe,Tokyo-to, Japan, assignors to Kokusai Denki Kabushiki Kaisha, Tokyo-to,Japan, a joint-stock company of Japan Filed Oct. 8, 1963, Ser. No.314,770

Claims priority, application Japan, Nov. 28, 1962,

37/52,163; Jan. 31, 1963, 38/4,099; Mar. 8, 1963,

38/10,573, 38/10,576 2 Claims. (Cl. 148-635) The present inventionrelates to techniques in the treatment of surfaces of materials,particularly iron and steel. More specifically, the invention relates tonew and improved method and means for sulphurizing surfaces of iron andsteel to effect surface treatment thereof.

Conventional methods for sulfurizing of iron and steel as practicedheretofore have been accompanied by certain difficulties anddeficiencies, particularly in the sulfurizing agents (hereinafterreferred to as sulfur penetrants) used, as will be describedhereinafter.

It is an object of the present invention, in its broader aspects, toovercome such difficulties and deficiencies experienced heretofore.

More specifically, it is an object of the present invention to provide anew and improved method of sulfurizing articles of iron and steel. Theinvention, in one aspect thereof, contemplates accomplishing suchsurface treatment through the use of a solid sulfur penetrant and, inanother aspect thereof, contemplates accomplishing the treatment throughthe use of a gaseous sulfur penetrant.

It is another object of the invention to provide new and improved sulfurpenetrants, particularly a solid sulfur penetrant, suitable for use inthe method of the invention.

It is still another object to provide new and improved apparatussuitable for practicing the method of the invention.

It is a further and general object to afford economy, convenience, andsimplicity of method and means and other advantages in the achievementof the objects of the invention.

The foregoing objects, as well as other objects and advantages as willpresently become apparent, have been achieved by the present invention,the nature and details of which will be best understood by reference tothe following description of preferred embodiments of the invention whentaken in conjunction with the accompanying drawing in which like partsare designated by like reference characters, and in which:

FIGURE 1 is an elevational view,.in vertical section, indicating oneembodiment of the method according to the invention;

FIGURE 2 is an elevational view, in vertical section, indicating anotherembodiment of the method of the invention; and

FIGURE 3 is an elevational view, in vertical section, showing anembodiment of apparatus suitable for the practice of the presentinvention.

In one of its aspects, the present invention provides a sulphurizingmethod which, briefly described, comprises burying an article to betreated in a powder mixture of, for example, a non-crystalline carbonpowder,

such as carbon powder produced from heavy oil having a high sulfurcontent, containing sulfur and hydrogen, and heating the same to atemperature between 400 and 600 degrees C.

In one embodiment of the invention, a graphite crucible 1, as shown inFIGURE 1, is filled with the noncrystalline carbon powder 2 producedfrom heavy oil having high sulfur content. An iron or steel material 3"ice constituting the metal article to be treated is buried in thispowder. A lid 4 is placed in position to cover the crucible 1, and asealing material 5 is applied to seal the seam between the cover 4 andthe crucible 1. The crucible 1 so prepared is then heated toapproximately 575 degrees C. and maintained at this temperature for acertain time, whereupon a sulfurized layer is formed on the surface ofthe material 3 so treated. The carbon powder, together with the treatedmetal article buried therein, is then cooled to a temperature belowdegrees C. before the article is removed from the crucible. This step istaken to prevent the article, while at a high temperature, fromcontacting O in the air.

To facilitate a clearer understanding of the abovedescribed process, aspecific example of its application is described below.

Example 1 A piece of iron designated by the trademark name of Armco ofl8-mm. diameter and 10-mm. thickness was buried in approximately 50grams of the above-mentioned carbon powder placed in and filling agraphite crucible and, after placement of the lid and sealing with thesealing material, was heated for 2 hours at the above-stated temperatureof 575 degrees C. The iron piece was thencooled, together with thecarbon powder, to a temperature below 100 degrees C. and then removedfrom the crucible. As a result, a sulfurizing layer of approximately 0.3mm. average thickness was obtained.

It was further found that the sulfur content of the carbon powder by theabove process reached approximately 3 percent, and the volumetriccontents of the gases generated by this sulfurcontent at 575 degrees C.were as follows: 6.92 percent H S; 1.5 percent S0 1.76 percent CS 17.3percent CO remainder N where 0 comes to the air occluded in the powder.

That is, the sulfur S becomes H 8, S0 and CS and, assuming the vaporphase without going through the liquid phase, acts on the article beingtreated. In this case, these gases dissociate under the catalytic actionof the iron material being treated to produce atomic-state sulfur. Thisatomic sulfur reacts with the iron material to form at least onesulfide, Fe S, and exhibits the so-called sul-' phurizing effect.

The reason for using a carbon powder prepared from heavy oil with a highsulfur content is that such a carbon powder makes possible low-costgeneration of H 8, S0 and CS which facilitate the generation of atomicsulfur. It will be obvious that such a carbon powder producedsynthetically with a sulfur content of the order of 1 to 3 percent canalso be used.

cost. In contrast, the sulfur penetrant according to the presentinvention is a solid which is easily handled and can be produced at lowcost.

Briefly described, the sulfur penetrant of the invention is composedessentially of carbon powder having fixed thereto principally hydrogenin the form of a quinone radial and sulfur content in the form of freesulfur.

One practical embodiment of the sulfur penetrant according to theinvention is a granulated amorphous carbon powder having a particle sizedistribution of approximately 30 to 100 meshes, an apparent (or bulk)specific gravity of approximately 0.27 to 0.4, a sulfur content ofapproximately 3 percent, and a quinone radical content of 0.6 percent.It has been found that when this sulfur penetrant is placed in agraphite crucible and heated to approximately 575 degrees C., thegenerated gas, on the basis of 100 cc., is composed of approximately 7.9percent of H 8, approximately 1.76 percent of CS 1.5 percent of S0 19.5percent of CO and remainder of N The presence of nitrogen and oxygen isdue to the air existing with the penetrant within the crucible.

In the case wherein only free sulfur is used, FeS is merely formed onthe surface of the iron or steel article, as is well known. This FeScontributes nothing to wear resistance for friction, which is thepurpose of sulfurizing treatment, but, rather, is detrimental to thearticle. It has been found that, on the other hand, the presence of Cand the H in the quinone radical causes the free S to become H 8 at therequired heating temperature, and this gas, H 8, upon contacting theiron or steel, causes the formation of a sulfurized layer of Fe S,thereby causing wear resistance to be exhibited. It has been foundfurther as a result of X-ray analysis that the value of this quantity 1xis approximately 0.9, wherefore the aforesaid molecule is Fe S.

The performance of the sulfur penetrant according to the invention hasbeen studied experimentally, and it has been found that, as one aspectof performance, the quantity of the penetrant necessary per one squarecentimeter of surface area to form a sulfurized layer of approximately(14 mm. thickness on the surface of an iron or steel article isapproximately grams.

The carbon powder of the invention as described above can be readilyproduced, for example, by oil cracking of a heavy 'oil having an amplyhigh sulfur content. Since the H obtained as a by-product during such aprocess can be advantageously utilized, the invention has theafore-mentioned advantage of low production cost.

In another embodiment of the method of the present invention, thesulfurizing of iron and steel is greatly improved through the use of H8, CS or a mixture of the two, and rapid sulfurizing treatment can beaccomplished.

An apparatus suitable for the practice of this embodiment comprises acrucible 1 (for example, of graphite), as indicated diagrammatically inFIGURE 2, provided in its interior with an intermediate shelf 5consisting of a gas-porous plate and a gas inlet pipe 7a for supplying HS gas into the chamber below the shelf 5. In the practice of thismethod, the space in the crucible 1 above the shelf 5 is filled withcarbon black 2, in which an article 3 to be treated is buried. Then, H 8gas is supplied through the gas inlet pipe 7a, through the shelf 5 inthe direction of the arrows X, and uniformly into the carbon black 2.The shelf is available to this purpose. The crucible 1 is heated to andmaintained at a suitable sulfurizing temperature, for example, 575degrees C. The crucible 1 may be heated by any suitable method, one suchmethod being to immerse the crucible in a carbon environment within anelectric furnace of the fluid particle type.

The above-described process will be better understood by considerationof the following example of typical application.

Example 2 50 grams of carbon black were placed in a graphite crucible onan intermediate gas-porous shelf, and a disk of so-called Armco materialof 18-min. diameter and 10-min. thickness was buried in the carbonblack. H 8 gas was supplied upwardly through the intermediate shelf intothe carbon black at a fiowrate of 0.1 liter per minute, and the cruciblewas heated for two hours at 575 degrees C. The disk was then cooled,together with the carbon black, to a temperature below 100 degrees C.and then removed from the crucible. As a result, a sulfurizing layer of(LS-mm. thickness having a composition of Fe S was obtained on thesurface of the disk.

In comparison, a sulfurizing layer of only 0.2-mm. thickness can beobtained by the conventional method, that is, the method wherein only HS gas is used without the use of carbon black. The reason for this isbelieved to be that the hydrogen released from H 8 during thesulphurizing treatment remains as spurious matter on the surface of thearticle being treated, and the apparent concentration of the H S isdiluted by this spurious hydrogen, whereas, when carbon black is presentas in the case of the present invention, this carbon black adsorbs thespurious hydrogen, Wherefore the sulfurizing effect is increasedaccordingly.

It has been found that, other than the H 5 for the process gas supplied,CS gas or a mixture of H 8 and CS gases produce equivalent results.

The present invention, in still another aspect thereof, provides anapparatus suitable for practicing the abovedisclosed method of theinvention.

As mentioned briefly hereinbefore, it is necessary, after the heatingprocess step of the method of this invention, to cool the treatedarticle, still in its position in the carbon powder within the crucible,until the temperature of the article has dropped to degrees C. or lowerand then to take it out since its contact with air while at a hightemperature is undesirable. The present invention provides an apparatuswhich is adapted to accomplish this cooling step in a simple andeffective manner. The details of this apparatus will now be describedwith respect to a preferred embodiment.

Referring to FIGURE 3, the essential parts of the apparatus are: acrucible 1 (for example, a graphite crucible) having a lid 4; agas-porous plate 5 horizontally disposed from wall to wall across theinterior of the crucible 1 with a space of height d between the lowersurface of the plate 5 and the bottom of the crucible 1; as gas inletpipe 7 extending downwardly through the lid 4, through the crucibleinterior space above the plate 5, and through the 5 into the spacetherebelow; and a gas exhaust pipe 6 provided through the lid 4. Theinlet and exhaust pipes 7 and 6 are provided, respectively, with valves9 and 10-. During operation, the space within the crucible 1, above theplate 5, is filled with a carbon powder, and an article to be treated isburied within this powder as has been described hereinbefore.

For the heating step of the method according to this invention, theabove'described combination of parts is heated by any suitable means. Inthe instant embodiment, this combination of parts is placed within andheated by a fluid carbon-particle, environmental medium 8 containedwithin the vessel 11 of a fluid-particle electric furnace.

The apparatus of the above-described construction is suitable forcarrying out the method according to the present invention asillustrated by Examples 1 and 2 set forth hereinbefore. In the case ofthe process of Example 1, the two valves 9 and 10 are kept closed duringthe heating step. In the case of the process of Example 2, the gas inletpipe 7 is used to supply H 8 gas into the carbon powder 2 upwardlythrough the gas-porous plate 5.

In either case, the valves 9 and 10 are opened after the beating step,and an inert gas (for example, nitrogen gas) is supplied at a certainflowrate and discharged through the gas exhaust pipe 6. It has beenfound that, in the case of the quantities specified in Examples 1 and 2,an inert gas supplied at a flowrate of 10 cc./minute rapidly cools thearticle 3 after heating treatment to a temperature below 100 degrees C.in approximately 15 minutes without causing any chemical reaction in thearticle 3 and the sulfur penetrant material 2.

It has been confirmed, further, that by the use of the above-describedapparatus in the above manner, there is no possibility of drawingoutside air into the crucible interior while the article 3 is still at ahigh temperature, and, moreover, that the surface of the article 3 takenout after cooling from the crucible is free of irregularities anddefects.

It should be mentioned that if the coolant gas is supplied directlywithout the use of the gas-porous plate 5,

the gas will concentrate locally and flow rapidly toward the opening ofthe gas exhaust pipe 6, wherefore the cooling effect Will be deficient.

It will be thus observed that the above-described apparatus according tothe invention of relatively simple construction and operation not onlymakes possible the practice of the method of this invention but alsoaffords rapid cooling thereafter of the article being treated withoutcausing oxidation thereof.

It should be understood, of course, that the foregoing disclosurerelates to only preferred embodiments of the invention and that it isintended to cover all changes and modifications of the examples of theinvention herein chosen for the purposes of the disclosure, which do notconstitute departures from the spirit and scope of the invention as setforth in the appended claims.

What is claimed is:

1. Method of sulfurizing iron and steel articles, com- References CitedUNITED STATES PATENTS 949,500 2/1910 Rees 148--6.35 1,5 62,13 8 11/ 1925Becker l486.24 2,874,480 2/ 1959 Todd.

2,914,432 11/1959 Singer 148-635 X 2,972,501 2/ 1961 Feinman.

ALFRED L. LEAVITT, Primary Examiner.

J. R. BA'ITEN, JR., Assistant Examiner.

1. METHOD OF SULFURIZING IRON AND STELL ARTICLES, COMPRISING BURYING THE ARTICLE IN AMORPHOUS CARBON POWDER CONTAINING SULFUR AND HYDROGEN AND HEATING THE POWDER TOGETHER WITH THE ARTICLE BURIED THEREIN AT A TEMPERATURE WITHIN THE RANGE OF FROM 400 TO 600*C. 